This invention relates to an orthopedic implant augmentation and stabilization device. More particularly, this invention relates to an apparatus which facilitates coupling of an augment to a surface of an orthopedic implant to compensate for bone loss while minimizing surgical time and manufacturing costs.
When installing prosthetic implants to replace joints such as in a total knee replacement operation, it is sometimes necessary to compensate for bone loss which can occur through wear or disease. Bone loss can also be caused by removal of previously installed implants.
It is known to provide spacing wedges or augments to compensate for bone loss and to prevent gaps between the bone and the surfaces of the prosthetic implants installed onto the bone. Current methods which are used to attach augments to the prosthetic implants includes screws, snap-fits, and the use of bone cement. The use of screws to hold the augments in place on the implant results in metal against metal contact. Micromotion between the augment and the implant after installation of the implant can cause metal fretting particles or metallic debris to be produced. This can cause an osteolytic reaction and loosening of the implant. It is also known to provide a snap-fit metal against metal contact. These snap-fit augments are allowed to wobble in place and can also produce metal frettings or metallic debris. In addition, it is known to use metal pegs in combination with bone cement to couple an implant to an augment. However, these known metal pegs also produce metal against metal contact which can cause an osteolytic reaction and loosening of the implant.
It is also known to use bone cement between the augments and the implant. Current systems that use bone cement to secure the augments in place do not use anything other than cement to keep the metallic components separated nor do the current systems provide any means for immediate fixation of the augment to the implant. The components cannot be implanted until the bone cement between the implant and the augment is cured. This results in extending the operating room time for the patient from about 15 minutes to about 45 minutes.
One object of the present invention is to provide an apparatus for attaching augments to implants to compensate for bone loss while minimizing surgical time, manufacturing costs, and the number of components necessary to perform surgery.
Another object of the present invention is to provide an apparatus for initially retaining a metal augment relative to a metal implant without producing any metal against metal contact to permit the implant to be installed onto the bone without waiting for bone cement to cure. In this apparatus, standoff means is provided for separating and positioning the metal augment relative to the metal implant while the bone cement cures, the standoff means comprising plastic means engaging the implant and the augment.
In one embodiment of the present invention, acrylic pegs or conical shapes are coupled to the metal implant via ultrasonic welding, interference fits, threads, or other coupling methods. The acrylic components can be used along with bone cement to secure and stabilize the augment relative to the implant. The acrylic components locate and stabilize augments such as tibial and femoral wedges in place until the bone cement between the two components is cured. Therefore, the components of the present invention provide temporary fixation between the augments and the implants until the bone cement cures. The acrylic pegs of the present invention can also provide temporary positioning of the implant relative to the bone until the bone cement cures between the implant and the bone. The acrylic pegs are used to resist movement during implantation. The acrylic pegs eliminate the metal-to-metal contact which is present in known devices. In addition, the acrylic pegs of the present invention can be easily cut and aid in removal of the device.
In another embodiment of the present invention, metallic pegs or projections are provided on the augment to increase the ability of the pegs to sustain higher shear loads. In this embodiment, the augments are provided with an integral square metal peg formed on top of a cylindrical boss. The square peg is designed to be interference fit with a plastic sleeve which is fitted into a hole formed in the implant to be augmented. The cylindrical boss engages the sleeve to provide a stand off to prevent metal against metal contact between the augment and the implant. The boss region is purposely designed to have a diameter smaller than the outside diameter of the sleeve to ensure that only the plastic sleeve contacts the boss. The square peg permits cement flow past the flat sides of the peg to eliminate the potential for cement pressure to build up and prevent seating of the augment.
According to one aspect of the present invention, a prosthesis is provided for replacing a bone surface. The prosthesis includes an implant having a surface for abutting a bone, and an augment configured to be attached to the surface of the implant by bone cement to compensate for bone loss. The augment is formed to include an aperture therein defined by an inner wall. The prosthesis also includes a plastic peg coupled to the implant. The peg is configured to enter the aperture formed in the augment and to engage the inner wall of the augment to retain the augment in a spaced apart relation relative to the implant to permit the implant to be installed onto the bone before the bone cement cures.
In one illustrated embodiment, the peg includes a generally conically shaped head coupled to the surface of the implant and a body portion extending away from the head of the peg. The head portion of the peg engages the inner wall of the augment to retain the augment relative to the implant.
The body portion of the peg extends through the aperture formed in the augment beyond a bottom surface of the augment opposite from the implant. The peg thereby provides means for aligning the prosthesis relative to the bone.
The prosthesis can include a second plastic peg or standoff means coupled to the implant spaced apart from the first plastic peg. The second plastic peg engages a top surface of the augment to provide a stand off to maintain the surface of the implant spaced apart from the top surface of the augment. Such a plastic peg or standoff means may be placed on the metal augment to engage the metal implant.
In another embodiment of the invention, the implant is formed to include an aperture therein and the peg is press fit into the aperture formed in the surface of the implant to couple the peg to the implant. The peg includes first and second conically shaped sections for engaging the implant and the augment, respectively.
According to another aspect of the invention, a prosthesis is provided for replacing a bone surface. The prosthesis includes an implant having a surface for abutting a bone. The surface of the implant is formed to include an aperture therein. The prosthesis also includes an augment configured to be attached to the surface of the implant by bone cement to compensate for bone loss, and a plastic retaining ring located in the aperture formed in the surface of the implant. The prosthesis further includes a metal peg coupled to the augment. The peg is configured to enter the aperture formed in the implant and to engage the plastic retaining ring therein to retain the augment in a spaced apart relation relative to the implant to permit the implant to be installed onto the bone before the bone cement cures.
In this illustrated embodiment, a boss is formed between the peg and the augment. The boss is configured to engage only a top surface of the plastic retaining ring so that the boss provides a stand off to maintain said spaced apart relation between the augment and the implant. The boss has a generally cylindrical shape. The boss has a predetermined diameter and the plastic retaining ring has a diameter larger than the predetermined diameter of the boss so that the boss only engages the plastic retaining ring.
A plastic peg may be coupled to the implant spaced apart from the aperture for receiving the metal peg if desired. The plastic peg engages a surface of the augment to provide a stand off to help maintain the implant in said spaced apart relation relative to the augment.
Alternately, a plastic peg may be coupled to the augment spaced apart from the metal peg if desired. The plastic peg engages a surface of the implant to provide a stand off to help maintain the implant in said spaced apart relation relative to the augment.
It is understood that the present invention can be used with tibial components, femoral components, or any other type of implant which may require augments. Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of the preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.